Because maybe speed and performance, as well as trends and fashion are just as important to some people as comfort and practicality.
Just because you commute to work on a bike doesn't mean you only want that bike for commuting. Many new riders move on to weekend riding, then club riding and sometimes racing. I've done all those things on the same bike.
When buying a car 20 years ago, alloy wheels were a bolt on luxury passed down from the racetrack for drivers who wanted to have a nicer looking car. Now they're commonplace, but arguably still a much more practical wheel than something steel with a plastic cap.
In the same way, most road bikes now come with a lower spoke count wheel, bladed spokes, deeper section rims etc because that's the fashion passed down from the racing world. If you're going to be going out on a club run you'll probably feel the benefit from that wheel, plus you'll get more admiring nods from your club mates. As wrong as many may think this is, acceptance, belonging, camaraderie and fitting in is a part of cycling for many.
Plus every single one of us is different. That's why there are many styles of bike for different individuals, not just for different occasions of riding. Some like to race on their commute. Strava has helped to breed this new kind of rider that benefits from lighter, aggressive set ups.
And while you may pour scorn over someone racing past others trying to obtain a KOM on the way to work, as long as it's done safely I very much support anything that makes someone wake up and feel excited about cycling rather than driving their car.
As an aside, some very fit and flexible riders are capable of finding comfort on any racing setup.
Although we all know that a bike isn't just a bike... to a large extent a bike IS just a bike. They're incredibly versatile and multi-functional. Setups can be adjusted for different purposes, wheels can be changed, racks and guards can be added - whether you have eyelets in a steel frame, or p clips or skewer adapters on a carbon frame.
What we're all after essentially is value for money, something that we enjoy looking at and riding on, and something that fulfils our requirements on the road, track, or trail.
I don't have the money, time or inclination to create one right now, although it's possibly a project for later in life, but I'm very much an advocate of the 'one bike for all occasions'. I don't think that is encapsulated better than this article:
http://www.cyclingweekly.co.uk/news/latest/538831/andy-wilkinson-s-dolan-time-trial-bike.html
So in summary, perhaps there is a responsibility to question an OP on their riding intentions a little more thoroughly, but the problem is that so many of us use such a wide variety of styles of bike and set up for such a wide variety of purposes that recommendations that seem very odd to some will be perfectly viable to others.